1. Field of the Invention
The present invention relates to a fuel cell system, and particularly, to a fuel cell system including a solid polymer electrolyte fuel cell which wastes hydrogen during a startup run of the system.
2. Description of Relevant Art
As countermeasures against recent environmental problems, particularly against such problems as air pollution due to exhaust gases from the vehicle, and global warming due to carbon dioxide, attention has been directed to fuel cell systems having clean waste gases and high energy efficiencies.
The fuel cell system is an energy converting system configured with one or more fuel cells each having a fuel electrode (anode) supplied with a gaseous fuel such as hydrogen and an oxidizer electrode (cathode) supplied with a gaseous oxidizer such as air, for promoting electrochemical reactions in between to convert chemical energy of the fuel into electrical energy to be output.
The fuel cell is categorized by its electrolyte. The solid polymer electrolyte fuel cell is a fuel cell using a solid polymer membrane as the electrolyte. This type of fuel cell can be made compact at low cost, allowing for high power density, and is employed in the most of fuel cell systems constituting a drive power source for vehicles.
For most fuel cells, the fuel is hydrogen, which is a flammable gas needing careful handling. Fuel cell systems provided with a fuel cell using hydrogen as the fuel emit a waste gas containing hydrogen, and need some countermeasures to control the concentration of hydrogen in the waste gas.
In particular, for fuel cell systems constituting a drive power source for vehicles, such countermeasures should have a sufficient effect not to emit a waste gas high of hydrogen concentration, outside a vehicle, for example.
There is a technique proposed from such a standpoint in Japanese Patent Application Laid-Open Publication No. 2004-55287 for a hydrogen purge for wasting hydrogen with mixed impurities such as nitrogen and moisture accumulated on the fuel electrode side during running of a fuel cell system, in which hydrogen wasted at the fuel electrode side is sufficiently diluted with air wasted at the oxidizer electrode side, to be emitted outside a vehicle.